A stent is a radially expandable endoprosthesis which is adapted to be implanted in a body lumen. Stents are typically used in the treatment of atherosclerotic stenosis in blood vessels and the like to reinforce body vessels and to prevent restenosis following angioplasty in the vascular system. They have also been implanted in urinary tracts, bile ducts and other bodily lumen. They may be self-expanding or expanded by an internal radial force, such as when mounted on a balloon.
Delivery and implantation of a stent is accomplished by disposing the stent about a distal portion of the catheter, percutaneously inserting the distal portion of the catheter in a bodily vessel, advancing the catheter in the bodily lumen to a desired location, expanding the stent and removing the catheter from the lumen. In the case of a balloon expandable stent, the stent is mounted about a balloon disposed on the catheter and expanded by inflating the balloon. The balloon may then be deflated and the catheter withdrawn. In the case of a self-expanding stent, the stent may be held in place on the catheter via a retractable sheath. When the stent is in a desired bodily location, the sheath may be withdrawn allowing the stent to self-expand.
In the past, stents have been generally tubular but have been composed of many configurations and have been made of many materials, including metals and plastic. Ordinary metals such as stainless steel have been used as have shape memory metals such as Nitinol and the like. Stents have also been made of biodegradable plastic materials. Stents have been formed from wire, tube stock, etc. Stents have also been made from sheets of material which are rolled.
A number of techniques have been suggested for the fabrication of stents and other tubular members from sheets and tubes. One such technique involves laser cutting a pattern into a sheet of material and rolling the sheet into a tube or directly laser cutting the desired pattern into a tube. Other techniques involve cutting a desired pattern into a sheet or a tube via chemical etching or electrical discharge machining.
Laser cutting of stents has been described in a number of publications including U.S. Pat. No. 5,780,807 to Saunders, U.S. Pat. No. 5,922,005 to Richter and U.S. Pat. No. 5,906,759 to Richter. Other references wherein laser cutting of stents is described include: U.S. Pat. No. 5,514,154; U.S. Pat. No. 5,759,192; U.S. Pat. No. 6,131,266 and U.S. Pat. No. 6,197,048.
In some instances, stents are tubular members that have been provided with a pattern of apertures or holes cut around the circumference of the tube along most of its length. The resulting stent is utilized to reinforce the walls of the artery or other body lumen to reinforce or prevent closing of the artery or lumen, or to at least prolong the time the artery takes to re-close. The pattern in a stent is typically cut or etched by a mechanical, chemical or laser cutting device.
In manufacturing stents, basic lathe techniques have been adapted to support the tubing used to form the stent during the hole cutting process. Some examples of such techniques and apparatuses used for implementing them are described in U.S. Pat. No. 5,026,965; U.S. Pat. No. 5,221,824; U.S. Pat. No. 5,744,778 and U.S. Pat. No. 6,114,653.
Typically, a piece of tubing is supported between a drive mechanism and a tail stock support in the manner of a lathe. A laser cutting tool positioned above the tubing will cut the pattern by moving relative to the tubing along the length of the finished stent, the tubing being rotated as necessary to present different parts of the circumference to the laser cutting tool.
This manufacturing method has various limitations which results in a fairly high scrap rate. For example, because the pattern typically occupies a large percentage of the surface area of the stent, the stent may sag or bow downwardly during the cutting process as the pattern is cut and the cut area becomes larger. This is particularly true for thin walled material of the type most desirably used to form stents. Accordingly, many stents are rejected as failing to meet the necessary cut accuracy when manufactured by the methods used prior to this invention.
Another limitation that some prior stent manufacturing processes are affected by is that many of the lathe or other rotary systems used in machining the stent tube often employ a live spindle bearing assembly that exits a rotary motor of significant mass. Such assemblies further include a head stock or collet closer having draw bar riding inside a set of ball bearings. A collet is attached to the draw bar and is actuated by a yoke mechanism, which in turn retracts the draw bar into a tapered sleeve. It is clear that such high mass assemblies and their associated components are prone to wear induced complications that may ultimately lead to an increased chance of partial or even complete system failure. Such degradation is implicitly related to the high cost of maintaining such systems.
All U.S. patents and applications and all other published documents mentioned anywhere in this application are incorporated herein by reference in their entirety.
Without limiting the scope of the invention a brief summary of some of the claimed embodiments of the invention is set forth below. Additional details of the summarized embodiments of the invention and/or additional embodiments of the invention may be found in the Detailed Description of the Invention below.
A brief abstract of the technical disclosure in the specification is provided as well only for the purposes of complying with 37 C.F.R. 1.72. The abstract is not intended to be used for interpreting the scope of the claims.